Display device

ABSTRACT

A self-luminescence display device, in which dispersion in display among a plurality of pixels, caused by dispersion in characteristics among drive thin-film transistors, is decreased and uniform display free of unevenness can be obtained. The device includes a plurality of pixels having current drive type luminescent elements, and parallel-connected n (n≧2) thin-film transistors to feed a drive current to the respective current drive type luminescent elements. The transistors are arranged in different pixels, respectively, for example, in a first region of pixels adjacent to one another along a first direction. A second region of dummy pixels can be provided on at least one side of said first region along said first direction.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a display device and, moreparticularly, to a structure of an active matrix type organicelectroluminescent display.

[0003] 2. Description of the Related Art

[0004] Active matrix driven organic electroluminescent displays(referred below to as AMOLED) is expected as flat panel displays of thenext generation succeeding conventional liquid crystal displays.

[0005] Conventionally, a two-transistor structured circuit, as disclosedin JP-A-2000-163014 (first prior technique), comprising a drivethin-film transistor (referred below to as EL drive TFT) for feedingcurrent to organic electroluminescent elements (referred below simply toas EL element), a holding capacitor connected to a gate electrode of theEL drive TFT for holding a picture signal voltage, and a switchthin-film transistor (referred below to as switch TFT) for feeding apicture signal voltage to the holding capacitor, has been known as afundamental pixel circuit for a pixel drive circuit of AMOLED.

[0006] The two-transistor structured fundamental pixel circuit causes asignificant problem that nonuniformity in a picture is caused bydispersion every pixel in a threshold voltage (Vth) and mobility (μ) ofthe EL drive TFT due to dispersion every location in the crystallizingproperty of a semiconductor thin film (for which a polycrystal siliconfilm is ordinarily used) constituting the EL drive TFT.

[0007] Since dispersion in threshold voltage and mobility results indispersion in a drive current value of the EL element, emissionintensity disperses to cause minute unevenness to be seen inrepresentation.

[0008] Such unevenness in representation becomes particularlyproblematic when a drive current value is small to represent half tone.

[0009] Several measures have been devised in order to suppress thatnonuniformity in representation, which is caused by such dispersion inthe characteristics of an EL drive TFT.

[0010] For example, JP-A-11-219133 discloses a method, in whichdispersion in a drive current value is suppressed by making channellength and channel width of an EL drive TFT fairly greater than anaverage crystal particle size of polycrystal silicon constituting the ELdrive TFT (referred below to as second prior technique).

[0011] Also, JP-A-2000-3305027 discloses a drive method by a so-calledpulse-width modulation, in which an EL drive TFT is driven as a binaryswitch for effecting a complete OFF state or a complete ON state andtone of a picture is represented by changing a duration of emission(referred below to as third prior technique).

[0012] Also, JP-A-11-73158 discloses an area tone system, in which aplurality of EL elements having different luminescent areas are providedin a unit pixel, and an EL drive TFT is connected to each of theplurality of EL elements and driven as a binary switch for effecting acomplete OFF state or a complete ON state, whereby tone is representedby changing luminescent areas (referred below to as fourth priortechnique).

[0013] Also, U.S. Pat. No. 6,229,506B1 discloses a method, in which fourTFTs are provided in a pixel to constitute a circuit for cancellingdispersion in a threshold voltage of an EL drive TFT whereby dispersionin drive current is decreased (referred below to as fifth priortechnique).

[0014] Also, JP-A-8-129359 discloses a method, in which a plurality ofEL drive TFTs having different current drive capacities conformed to aplurality of tone currents are connected in parallel to one EL elementwithin each pixel and driven as binary switches for effecting a completeOFF state or a complete ON state, whereby tone representation iscontrolled by tone currents supplied from the plurality of EL drive TFTs(referred below to as sixth prior technique).

[0015] Also, JP-A-2000-221903 discloses a method, in which two EL driveTFTs are provided in a pixel to decrease dispersion in thresholdvoltages in the EL drive TFTs, thereby reducing dispersion in drivecurrent (referred below to as seventh prior technique).

[0016] However, the prior techniques described above involve thefollowing problems.

[0017] The second prior technique is directed to averaging dispersionevery location in the crystallizing property of the polycrystal siliconby increasing TFT size.

[0018] However, even when TFT size is increased, it cannot be madegreater than pixel pitch.

[0019] Accordingly, since a size of an EL drive TFT for driving an ELelement, which constitutes each pixel, is limited within an area of apixel, and the crystallizing property of a polycrystal silicon filmdisperses every location, it is not possible to compensate fordispersion between the characteristics of an EL drive TFT in aparticular pixel and the characteristics of an EL drive TFT in a pixeladjacent the particular pixel.

[0020] It is to be noted that what can be averaged by increasing a TFTsize is only dispersion in crystals sized within the TFT size.

[0021] Accordingly, it is difficult in the second prior technique toobtain a fairly uniform property of representation.

[0022] For the effect of averaging picture representation with the thirdprior technique, the pulse-width modulation driving is one of validmethods as an AMOLED driving method as having already been proved.

[0023] However, known as an essential problem in this driving method isbleeding in a picture generated when animation called pseudo-profile isrepresented because tone representation is made by luminescence pulse,which is developed on time base.

[0024] Also, because of a need for processing a short signal pulseconformed to digital tone, there is caused a problem that the drivecircuit is increased in operation frequency and power consumption.

[0025] Also, there is also caused a problem that a vertical scanningcircuit, which may ordinarily be a simple circuit, becomes complex and acircuit area is increased.

[0026] The fourth prior technique is much effective in uniformizingpicture representation, but multitone is difficult since it is necessaryto form in a unit pixel EL elements having areas conformed to digitaltone and to form EL drive TFTs corresponding to the respective ELelements.

[0027] Also, it has been known that EL elements are ordinarily decreasedin luminescent areas together with operation duration.

[0028] In the case of using EL elements having different luminescentareas, deterioration is caused with time beginning with an EL element,which has a small area corresponding to a low-tone bit, thus causingalso a problem that normal tone becomes difficult with time.

[0029] With the fifth prior technique, the provision of a circuit forcanceling dispersion in threshold voltage of an EL drive TFTnecessitates a wiring, which is not necessary in a conventionaltwo-transistor configuration, so that a decrease in numerical apertureand yield in manufacture causes a problem.

[0030] Also, what can be cancelled is only dispersion in thresholdvoltage, and dispersion in mobility remains intact. Therefore, there iscaused a problem that no fairly uniformizing effect is obtained on drivecurrent.

[0031] With the sixth prior technique, a plurality of EL drive TFTshaving current drive capacities conformed to digital tone are connectedin parallel.

[0032] However, it is apparent that normal tone representation is madedifficult when the plurality of EL drive TFTs disperse incharacteristics.

[0033] Also, since the plurality of EL drive TFTs are formed in a singlepixel in this method, the technique is in no way effective in decreasingdispersion in representation among a plurality of pixels.

[0034] With the seventh prior technique, dispersion in drive current canbe decreased in the case where one of two EL drive TFTs connected inparallel is varied in characteristics, but dispersion in drive currentcannot be decreased in the case where both the two EL drive TFTs arevaried in characteristics, and besides the two EL drive TFTs are formedin a single pixel, so that the technique is in no way effective indecreasing dispersion in representation among a plurality of pixels.

SUMMARY OF THE INVENTION

[0035] The invention has been thought of in order to solve the problemsof the above prior art, and has its object to provide a technique fordisplay devices, in which dispersion in representation among a pluralityof pixels, attributable to dispersion in characteristics of drivethin-film transistors is decreased and uniform representation free ofunevenness can be obtained.

[0036] Also, another object of the invention is to provide a techniquecapable of decreasing voltage drop and power consumption caused byresistance of taken-out wirings of cathode electrodes in a displaydevice.

[0037] The above and other objects and novel features of the inventionwill be made apparent from the descriptions in the specification of thisapplication and the accompanying drawings.

[0038] An outline of a typical one of the inventions disclosed in thisapplication will be simply described below.

[0039] That is, the invention has a feature in that a plurality of ELdrive TFTs are connected in parallel to current drive type luminescentelements arranged in respective pixel regions, current is supplied tothe current drive type luminescent elements from a plurality of currentsupply sources, and the plurality of EL drive TFTs are arranged in aplurality of pixel regions at intervals corresponding substantially topitch of pixel.

[0040] The plurality of EL drive TFTs are connected in parallel wherebyit is possible to average dispersion in drive current, attributable todispersion in threshold voltage and mobility among the plurality of ELdrive TFTs.

[0041] However, only making EL drive TFTs in plural and in parallel doesnot assure averaging dispersion in drive current for an EL drive TFTcorresponding to a particular pixel and, for example, pixels adjacent tothe particular pixel.

[0042] Nonuniformity in representation is caused by dispersion in drivecurrent for EL drive TFTs in a plurality of pixels, which dispersion isattributable to dispersion in the crystallizing property of asemiconductor film constituting TFTs and spatial dispersion in filmynature of an insulating film.

[0043] Since EL drive TFTs are arranged regularly at the same intervalsas array pitch of pixels, it may be thought that dispersion in drivecurrent is attributable to dispersion in the crystallizing property of asemiconductor film and spatial dispersion in filmy nature of aninsulating film on a scale of array pitch of pixels.

[0044] In order to average such dispersion, it is effective to spatiallydisperse and arrange the plurality of EL drive TFTs at array pitch ofpixels.

[0045] Accordingly, a plurality of EL drive TFTs are connected inparallel to current drive type luminescent elements arranged inrespective pixel regions, current is supplied to the current drive typeluminescent elements from a plurality of current supply sources, and theplurality of EL drive TFTs are arranged in a plurality of pixel regionsat intervals corresponding substantially to pitch of pixel, wherebydispersion in drive current supplied to the current drive typeluminescent elements corresponding to respective pixels can be decreasedand representation can be averaged.

[0046] The more the averaging effect by means of the plurality of ELdrive TFTs distributed and arranged spatially, the more the number ofTFTs connected in parallel.

[0047] It is theoretically predicted that the magnitude of dispersion indrive current decreases inversely proportional to {square root}N with anincrease in N when the number in parallel is N. Since pixels are limitedin size, N=2 to 12 is a practical value according to the rule of fineprocessing thin-film transistors (TFT) in the present circumstances.

[0048] Also, when the number of TFTs in a pixel is increased, it isdifficult to ensure an area for EL elements, which contribute toemission of light.

[0049] According to the invention, numerical aperture is enhanced byproviding a reflective layer in a manner to cover at least a part of ELdrive TFTs and forming current drive type luminescent elements on thereflective layer.

[0050] Also, since current from the luminescent elements in all pixelsflows through taken-out wirings of cathode electrodes of current drivetype luminescent elements arranged in respective pixel regions, it isimportant to decrease resistance of the taken-out wirings.

[0051] According to the invention, voltage drop and power consumptioncaused by resistance of taken-out wirings are minimized by shorteninglengths of the taken-out wirings, which are connected electrically tocathode electrodes of a plurality of current drive type luminescentelements, extending from an external connection terminal to a contactarea.

[0052] Concrete examples will be shown in the following embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053]FIG. 1 is a circuit diagram showing equivalent networks for pixelsin a display device according to a first embodiment of the invention;

[0054]FIG. 2 is a plan view showing a pixel arrangement in the displaydevice according to the first embodiment of the invention;

[0055]FIG. 3 is a circuit diagram showing an entire display unitincluding equivalent networks and a driving circuit in a matrix displaysection of the display device according to the first embodiment of theinvention;

[0056]FIG. 4 is a circuit diagram showing equivalent networks for pixelsin a display device according to a second embodiment of the invention;

[0057]FIG. 5 is a plan view showing a pixel arrangement in the displaydevice according to the second embodiment of the invention;

[0058]FIG. 6 is a circuit diagram showing an entire display unitincluding equivalent networks and a driving circuit in a matrix displaysection of the display device according to the second embodiment of theinvention;

[0059]FIG. 7 is a cross sectional view showing a cross-sectionalstructure cut along the line X-X′ shown in FIG. 5;

[0060]FIG. 8 is a cross sectional view showing a cross-sectionalstructure cut along the cut line Y-Y′ shown in FIG. 5;

[0061]FIG. 9 is a cross sectional view showing a cross-sectionalstructure cut along the cut line Z-Z′ shown in FIG. 5;

[0062]FIG. 10 is a circuit diagram showing equivalent networks forpixels in a display device according to a third embodiment of theinvention;

[0063]FIG. 11 is a plan view showing a pixel arrangement in the displaydevice according to the third embodiment of the invention;

[0064]FIG. 12 is a circuit diagram showing equivalent networks forpixels in a display device according to a fourth embodiment of theinvention;

[0065]FIG. 13 is a plan view showing a pixel arrangement in the displaydevice according to the fourth embodiment of the invention;

[0066]FIG. 14 is a cross sectional view showing a cross-sectionalstructure cut along the line X-X′ shown in FIG. 13;

[0067]FIG. 15 is a graph indicating the relationship between the numberN of thin-film transistors for driving parallel organicelectroluminescence elements and dispersion in luminance among pixels;

[0068]FIG. 16 is a plan view showing an entire configuration of displaydevices according to the respective embodiments of the invention;

[0069]FIG. 17 is an exploded, perspective view showing an entireconfiguration of display devices according to the respective embodimentsof the invention;

[0070]FIG. 18 is a cross sectional view showing an essential part of across-sectional structure of display devices according to the respectiveembodiments of the invention;

[0071]FIG. 19 is a view illustrating the manufacturing process of thedisplay device according to the second embodiment of the invention;

[0072]FIG. 20 is a view illustrating the manufacturing process of thedisplay device according to the second embodiment of the invention;

[0073]FIG. 21 is a view illustrating the manufacturing process of thedisplay device according to the second embodiment of the invention;

[0074]FIG. 22 is a view illustrating the manufacturing process of thedisplay device according to the second embodiment of the invention;

[0075]FIG. 23 is a view illustrating the manufacturing process, of thedisplay device according to the second embodiment of the invention;

[0076]FIG. 24 is a view illustrating the manufacturing process of thedisplay device according to the second embodiment of the invention;

[0077]FIG. 25 is a view illustrating the manufacturing process of thedisplay device according to the second embodiment of the invention;

[0078]FIG. 26 is a view illustrating the manufacturing process of thedisplay device according to the second embodiment of the invention; and

[0079]FIG. 27 is a view illustrating the manufacturing process of thedisplay device according to the second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0080] Embodiments according to the invention will be described indetail with reference to the drawings.

[0081] In addition, the same numerals and letters denote elements havingthe same functions in all the drawings, which illustrate embodiments,and repeated explanations therefor are omitted.

[0082] First Embodiment

[0083]FIG. 1 is a circuit diagram showing equivalent networks for pixelsin a display device according to a first embodiment of the invention,and FIG. 2 is a plan view showing a pixel arrangement in the displaydevice according to the first embodiment of the invention.

[0084] In a self-luminescence display device according to the invention,organic electroluminescent elements (referred simply below to as ELelements) of respective pixels are driven by three drive thin-filmtransistors (referred below to as EL drive TFT) provided on differentpixel regions.

[0085] In the first embodiment, respective EL drive TFTs are arranged inan associated pixel, the next pixel on the right side and the furthernext pixel but one on the right side.

[0086] In FIG. 1, there are shown three pixel regions surrounded byscanning signal wiring electrodes (Gm, G(m+1)), picture signal wiringelectrodes (Dn to D(n+1)), and anode current feeding wiring electrodes(A(n−1) to A(n+2)), which constitute a part of a TFT matrix.

[0087] A pixel in a row m and a column n is defined by a regionsurrounded by scanning signal wiring electrodes (Gm, G(m+1)), a picturesignal wiring electrodes Dn, and an anode current feeding wiringelectrode An.

[0088] Formed in respective pixels are switch thin-film transistors(referred below to as switch TFT) (Qs(m, n)), three EL drive TFTs(Qd1(m, n), Qd2(m, n), Qd3(m, n)), and a charge-storage capacitanceCst(m, n).

[0089] An anode electrode of an EL element OLED(m, n) is connected to adrain electrode of the EL drive TFT (Qd1(m, n)) via an EL connectionwiring electrode 15.

[0090] The EL element OLED(m, n) belonging to a pixel in row m andcolumn n is connected not only to the EL drive TFT (Qd1(m, n)) in thepixel but also in parallel to the EL drive TFT (Qd2(m, n+1)) formed inan adjacent pixel in row m and column (n+1) and the EL drive TFT (Qd3(m,n+2)) formed in an pixel in row m and column (n+2) such that current isfed from three anode current feeding wiring electrodes (An, A(n+1),A(n+2)).

[0091] All gate wiring electrodes 14 of the three parallel-connected ELdrive TFTs are connected to a drain electrode of a switch TFT (Qs(m, n))of a pixel in row m and column n via an EL connection wiring electrode12.

[0092] Also, a charge-storage capacitance Cst (m, n+2) is formed betweengate electrode nodes of the three EL drive TFTs and the anode currentfeeding wiring electrode A(n+2) to be able to keep voltage of the gatewiring electrodes 14 for a predetermined period of time.

[0093] In the embodiment, scanning signal wiring electrodes G aresequentially scanned, and a switch TFH (Qs), to which a scanning signalwiring electrode G made at H level is connected, is made ON.

[0094] Thereby, a picture signal voltage is fed via the switch TFH (Qs)to a charge-storage capacitance Cst from the picture signal wiringelectrodes Dn to be held on the charge-storage capacitance Cst.

[0095] Based on the picture signal voltage held on the charge-storagecapacitance Cst, the respective EL drive TFTs (Qd1, Qd2, Qd3) feed tothe EL elements OLED current corresponding to the picture signal voltageheld on the charge-storage capacitance Cst during one frame.

[0096] Thereby, the EL elements OLED emit light to display a pictureimage.

[0097] In addition, with the embodiment, gate length, channel length,and channel width are set so that current fed to the respective EL driveTFTs (Qd1, Qd2, Qd3) becomes substantially equal to a current fed by asingle EL drive TFT.

[0098] In the embodiment, the respective EL drive TFTs (Qd1(m, n),Qd2(m, n), Qd3(m, n)) are of a double gate structure to have a gatelength of 10 μm, total channel length of 20 μm, and a channel width of 4μm.

[0099] Supplying of current to the EL elements OLED(m, n) from the ELdrive TFT (Qd2(m, n+1)) and the EL drive TFT (Qd3(m, n+2)) is made byextending p+type semiconductor layers, which constitute sourceelectrodes and drain electrodes of the respective EL drive TFTs, as theyare and using the same as wiring.

[0100] With such configuration, since formation of surplus contactthrough holes is made unnecessary, surface efficiency is enhanced withthe result that numerical aperture is improved.

[0101] Take again notice of a pixel in row m and column n, the EL driveTFT (Qd2(m, n)) among the three EL drive TFTs (Qd1(m, n), Qd2(m, n),Qd3(m, n)) is provided to drive an EL element OLED(m, n−1) of a pixel inrow m and column (n−1), and the EL drive TFT (Qd3(m, n)) is provided todrive an EL element OLED(m, n−2) of a pixel in row m and column (n−2).

[0102] Also, the charge-storage capacitance Cst(m, n) is provided tohold an electric potential of a gate electrode node of the EL drive TFT(Qd3(m, n)).

[0103] The EL elements are formed on ITO electrodes (anode electrodes ofthe EL elements) 13, which are connected to the EL connection wiringelectrodes 15 via contact through holes, through openings formed onorganic insulating films 23.

[0104]FIG. 3 is a circuit diagram showing an entire display unitincluding equivalent networks and a driving circuit in a matrix displaysection of the display device according to the first embodiment.

[0105] As shown in FIG. 3, the matrix display section is composed of 600scanning signal wiring electrodes G1 to G600, 2400 picture signal wiringelectrodes D1R to D800R, D1G to D800G, and D1B to D800B, 2400 anodecurrent feeding wiring electrodes A1R to A800R, A1G to A800G, and A1B toA800B, and pixels provided in regions where these electrodes intersect.

[0106] The matrix display section is driven by a vertical scanningcircuit VDRV and a picture signal circuit HDRV, and the anode currentfeeding wiring electrodes arranged on the respective pixels areshort-circuited outside the regions of pixels to be connected to anexternal electric power source.

[0107] In the embodiment, since the EL drive TFTs are arranged in anassociated pixel, the next pixel on the right side and the further nextpixel, two rows of dummy regions of pixels are provided outside arightmost row of pixels.

[0108] Further, two anode current feeding wiring electrodes (A02, A03)are provided corresponding to the two rows of dummy regions of pixelsoutside the rightmost row of pixels.

[0109] Thus three anode current feeding wiring electrodes can also feeda specified current to the rightmost row of pixels via three EL driveTFTs.

[0110] Here, three pixels, in which three EL drive TFTs are arranged asshown in FIG. 3, are ones arranged in the same direction as a laserscanning direction of laser used when EL drive TFTs are manufactured.

[0111] In this manner, EL drive TFTs are scattered to be arranged in aplurality of pixels, and connected in parallel to drive one EL element,whereby current for the EL drive TFTs is averaged and so dispersion indrive current between pixels can be reduced to improve uniformity indisplay.

[0112] Also, since three anode current feeding wiring electrodes feedcurrent to one EL element via three EL drive TFTs at the same time,redundancy is provided for deficiency in display, which is caused bybreaking of anode current feeding wiring electrodes and failure inopening of EL drive TFTS, thus enabling enhancing yield in manufacture.

[0113] Second Embodiment

[0114]FIG. 4 is a circuit diagram showing equivalent networks for pixelsin a display device according to a second embodiment of the invention,and FIG. 5 is a plan view showing a pixel arrangement in the displaydevice according to the second embodiment of the invention.

[0115] As described above, with the self-luminescence display deviceaccording to the invention, EL elements of respective pixels are drivenby three EL drive TFTs provided on different pixel regions.

[0116] In the embodiment, respective EL drive TFTs are arranged in anassociated pixel, and the next pixels on the right and left sides.

[0117]FIG. 4 shows three regions of pixels surrounded by scanning signalwiring electrodes (Gm, G(m+1)), picture signal wiring electrodes (D(n−1)to D(n+2)), anode current feeding wiring electrodes (A(n−2) to A(n+1)),which constitute a part of the matrix.

[0118] A pixel in row m and column n is defined by a region, which issurrounded by scanning signal wiring electrodes (Gm, G(m+1)), a picturesignal wiring electrode Dn and an anode current feeding wiring electrodeAn, and there are formed in the pixel a switch TFT (Qs(m, n)), three ELdrive TFTs (Qd1(m, n), Qd2(m, n), Qd3(m, n)), and a charge-storagecapacitance Cst(m, n).

[0119] An anode electrode of an EL element OLED(m, n) is connected to adrain electrode of the EL drive TFT (Qd2(m, n)) via an EL connectionwiring electrode 15.

[0120] An EL element OLED(m, n) belonging to a pixel in row m and columnn is connected not only to the EL drive TFT (Qd2(m, n)) in the pixel butalso in parallel to an EL drive TFT (Qd3(m, n+1)) formed in an adjacentpixel in row m and column (n+1) and an EL drive TFT (Qd1(m, n−1)) formedin an pixel in row m and column (n−1) such that current is fed fromthree anode current feeding wiring electrodes (A(n−1), An, A(n+1)).

[0121] All gate wiring electrodes 14 of the three parallel-connected ELdrive TFTs are connected to a drain electrode of a switch TFT (Qs(m, n))of a pixel in row m and column n via an EL connection wiring electrode12.

[0122] Also, a charge-storage capacitance Cst (m, n+1) is formed betweengate electrode nodes of the three EL drive TFTs and the anode currentfeeding wiring electrode A(n+1) to be able to keep voltage of the gatewiring electrodes 14 for a predetermined period of time.

[0123] With the embodiment, gate length, channel length, and channelwidth are set so that current fed to the respective EL drive TFTs (Qd1,Qd2, Qd3) becomes substantially equal to a current fed by a single ELdrive TFT.

[0124] In the embodiment, the respective EL drive TFTs (Qd1(m, n),Qd2(m, n), Qd3(m, n)) are of a double gate structure to have a gatelength of 10 μm, total channel length of 20 μm, and a channel width of 4μm.

[0125] Supplying of current to the EL elements OLED(m, n) from the ELdrive TFT (Qd1(m, n−1)) and the EL drive TFT (Qd3(m, n+1)) is made byextending p+type semiconductor layers, which constitute sourceelectrodes and drain electrodes of the respective EL drive TFTs, as theyare and using the same as wiring.

[0126] With such configuration, since formation of surplus contactthrough holes is made unnecessary, surface efficiency is enhanced withthe result that numerical aperture is improved.

[0127] Taking again notice of a pixel in row m and column n, the ELdrive TFT (Qd1(m, n)) among the three EL drive TFTs (Qd1(m, n), Qd2(m,n), Qd3(m, n)) is provided to drive an EL element OLED(m, n+1) of apixel in row m and column (n+1), and the EL drive TFT (Qd3(m, n)) isprovided to drive an EL element OLED(m, n−1) of a pixel in row m andcolumn (n−1).

[0128] Also, the charge-storage capacitance Cst(m, n) is provided tohold an electric potential of a gate electrode node of the EL drive TFT(Qd3(m, n)).

[0129] The EL elements are formed on ITO electrodes (anode electrodes ofthe EL elements) 13, which are connected to the EL connection wiringelectrodes 15 via contact through holes, through openings formed on anorganic insulating film 23.

[0130]FIG. 6 is a circuit diagram of an entire display unit includingequivalent networks and a driving circuit in a matrix display section ofthe display device according to the second embodiment.

[0131] As shown in FIG. 6, the matrix display section is composed of 600scanning signal wiring electrodes G1 to G600, 2400 picture signal wiringelectrodes D1R to D800R, D1G to D800G, and D1B to D800B, 2400 anodecurrent feeding wiring electrodes A1R to A800R, A1G to A800G, and A1B toA800B, and pixels provided in regions where these electrodes intersect.

[0132] The matrix display section is driven by a vertical scanningcircuit VDRV and a picture signal circuit HDRV, and the anode currentfeeding wiring electrodes arranged on the respective pixels areshort-circuited outside the regions of pixels to be connected to anexternal electric power source.

[0133] In the embodiment, since the EL drive TFTs are arranged in anassociated pixel, and the next pixels on the right and left sides, tworows of dummy regions of pixels are provided on both sides of leftmostand rightmost rows of pixels, respectively.

[0134] Further, two anode current feeding wiring electrodes (A00, A01)are provided corresponding to the dummy pixels formed on the leftmostand rightmost rows of pixels.

[0135] Thus three anode current feeding wiring electrodes can also feeda specified current to the leftmost and rightmost row of pixels viathree EL drive TFTs.

[0136] In this manner, EL drive TFTs are scattered to be arranged in aplurality of pixels, and connected in parallel to drive one EL element,whereby current for the EL drive TFTs is averaged and so dispersion indrive current between pixels can be reduced to improve uniformity indisplay.

[0137] Also, since three anode current feeding wiring electrodes feedcurrent to one EL element via three EL drive TFTS at the same time,redundancy is provided for deficiency in display, which is caused bybreaking of anode current feeding wiring electrodes and failure inopening of EL drive TFTS, thus enabling enhancing yield in manufacture.

[0138] In the embodiment, the number of EL drive TFTs arranged inparallel is three, and the EL drive TFTS are arranged in an associatedpixel, and the next pixels on the right and left sides.

[0139] In comparing with the embodiment described above, lengths of thecurrent feeding wiring electrodes constituted by p+type semiconductorlayers from the EL drive TFT (Qd1(m, n−1)) and the EL drive TFT (Qd3(m,n+1)) to the EL element OLED(m, n) can be made substantially the same.

[0140] Thereby, sums of wiring resistances of the EL drive TFT and thep+type semiconductor layers from the anode current feeding wiringelectrode A(n+1) and the anode current feeding wiring electrode A(n+1)to the EL element OLED(m, n) can be made substantially the same.

[0141] Since the wiring resistance of the p+type semiconductor layers isordinarily set to be lower than the ON resistance of the EL drive TFT,unbalance in the wiring resistance of the p+type semiconductor layerscauses no significant problem but an error is caused when wiring lengthis increased.

[0142] An error due to unbalance in the wiring resistance of the p+typesemiconductor layers can be minimized by arranging EL drive TFTs in thenext pixels on both sides as in the embodiment.

[0143]FIG. 7 is a cross sectional view showing a cross-sectionalstructure cut along the line X-X′ shown in FIG. 5.

[0144] As shown in FIG. 7, a buffer Si₃N₄ film 200 having a thickness of50 nm and a buffer SiO₂ film 2 having a thickness of 100 nm are formedon a non-alkali glass substrate 1 having a thickness of 0.5 mm and astrain temperature of about 670° C.

[0145] These buffer insulating films (200, 2) serve to preventdispersion of impurities, such as Na or the like, from the glasssubstrate 1.

[0146] Formed on the buffer SiO₂ film 2 is a polycrystal Si (referredbelow to as poly-Si) film 30 having a thickness of 50 nm andcorresponding to the charge-storage capacitance Cst (m, n), and formedon the poly-Si film 30 through a gate insulating film 20 formed fromSiO₂ are gate wiring electrodes 14 of the EL drive TFTs composed of Mo.

[0147] Anode current feeding wiring electrodes An are formed on the gatewiring electrodes 14 of the EL drive TFTs through an interlayerinsulating film 21 composed of SiO₂, and are of a three-layeredelectrode structure composed of Mo (110 a), Al (110 b), and Mo (110 c).

[0148] Here, the gate wiring electrode 14 of the EL drive TFT (Qd3(m,n)) shown in FIG. 7 is shown as its portion being extended below theanode current feeding wiring electrode An such that the gate wiringelectrode 14 of the EL drive TFT (Qd3(m, n)) overlaps the anode currentfeeding wiring electrode An as shown in FIG. 5.

[0149] Also, the poly-Si film 30 shown in FIG. 7 is formed to overlapthe anode current feeding wiring electrode An as shown in FIG. 5, andthe poly-Si film 30 is electrically connected to the anode currentfeeding wiring electrode An via a contact hole (CHO in FIG. 5).

[0150] Accordingly, in the embodiment, the charge-storage capacitanceCst(m, n) is defined by a capacitative element formed by the interlayerinsulating film 21 between the anode current feeding wiring electrode Anand the gate wiring electrode 14, and a capacitative element formed by agate insulating film 20 between the gate wiring electrode 14 and thepoly-Si film 30.

[0151] In this manner, pixels are improved in numerical aperture byforming the charge-storage capacitance Cst(m, n) below the anode currentfeeding wiring electrode An.

[0152] Also, picture signal wiring electrodes (Dn, D(n+1)) are alsoformed on the same layer as the anode current feeding wiring electrodeAn, and the picture signal wiring electrodes (Dn, D(n+1)) are of athree-layered electrode structure composed of Mo (11 a), Al (11 b), andMo (11 c).

[0153] All these constituents are covered by a protective insulatingfilm 22 having a film thickness of 200 nm and composed of Si₃N₄, onwhich film is formed an anode electrode 13 composed of an indium-tinoxide (ITO).

[0154] Further, an organic insulating film 23 having a film thickness of2 μm and containing polyimide as its main component is formed on theanode electrode 13, and the organic insulating film 23 is providedsubstantially centrally of the anode electrode 13 with an opening.

[0155] Formed on the anode electrode 13 and the organic insulating film23 is an electron hole transport layer 300 having a film thickness of150 nm and composed of triphenyldiamine (TPD), and formed on the layerare a red EL luminescent layer 301R composed of a tris(8-hydroxyquinoline) aluminum (Alq3) having a film thickness of 30 nmand doped with DCJTB and rubrene, and an electron transport layer (notshown) having a film thickness of 30 nm and composed of Alq3.

[0156] Formed above the electron transport layer through LiF having afilm thickness of 0.8 nm is a cathode electrode 302 having a filmthickness of 150 nm.

[0157] Electron holes injected from the anode electrode 13 and electronsinjected from the cathode electrode 302 make radiational reunion in thered EL luminescent layer 301R to cause emission.

[0158] Light generated is emitted toward the glass substrate 1.

[0159] Arranged in adjacent pixels are blue dots and green dots, onwhich a blue EL luminescent layer 301B and a green EL luminescent layer301G are formed in place of a red EL luminescent layer.

[0160] The blue EL luminescent layer 301B is DPVBi doped with BCzVBihaving a film thickness of 15 nm, and the green EL luminescent layer301G is Alq3 doped with coumarin 540 having a film thickness of 30 nm.

[0161]FIG. 8 is a cross sectional view showing a cross-sectionalstructure cut along the cut line Y-Y′ shown in FIG. 5, and FIG. 9 is across sectional view showing a cross-sectional structure cut along thecut line Z-Z′ shown in FIG. 5.

[0162] As described above, the buffer Si₃N₄ film 200 having a thicknessof 50 nm and the buffer SiO₂ film 2 having a thickness of 100 nm areformed on the non-alkali glass substrate 1, the poly-Si film 30 having athickness of 50 nm and corresponding to the switch TFT (Qs(m, n)) andthe EL drive TFT (Qd2(m, n)) is formed on the films, and the scanningsignal wiring electrodes Gm and the gate wiring electrodes 14 of the ELdrive TFTs are formed on the poly-Si film 30 through the gate insulatingfilm 20 formed from SiO₂.

[0163] Here, the scanning signal wiring electrodes Gm are formed fromMo.

[0164] The switch TFT (Qs(m, n)) is composed of a N type TFT, thepicture signal wiring electrode Dn is connected to a source electrode ofthe switch TFT through a contact hole opened to the interlayerinsulating film 21, and the connection wiring electrode 12 is connectedto a drain electrode of the switch TFT.

[0165] As described above, the picture signal wiring electrode Dn is ofa three-layered electrode structure composed of Mo (11 a), Al (11 b),and Mo (11 c), and likewise the connection wiring electrodes 12 are of athree-layered electrode structure composed of Mo (12 a), Al (12 b), andMo (12 c).

[0166] The other of the connection wiring electrodes 12 is alsoconnected to the gate wiring electrodes 14 of the EL drive TFTs viathrough holes formed in the interlayer insulating film 21, so that asignal voltage of the picture signal wiring electrode Dn is applied tothe gate wiring electrode 14 of the EL drive TFT via the switch TFT(Qs(m, n)).

[0167] Meanwhile, the EL drive TFT (Qd2(m, n)) is composed of a PtypeTFT, to a source electrode of which the anode current feeding wiringelectrode An is connected via a contact hole opened to the interlayerinsulating film 21.

[0168] As described above, the anode current feeding wiring electrode Anis of a three-layered electrode structure composed of Mo (110 a), Al(110 b), and Mo (110 c).

[0169] A drain electrode of the EL drive TFT (Qd2(m, n)) is made commonto drain electrodes of the EL drive TFT (Qd1(m, n−1)) and the EL driveTFT (Qd3(m, n+1)), which are adjacent to the EL drive TFT (Qd2(m, n)),to be connected to the EL connection wiring electrode 15.

[0170] Here, the EL connection wiring electrodes 15 are of athree-layered electrode structure composed of Mo (15 a), Al (15 b), andMo (15 c).

[0171] Also, the anode electrodes 13 are connected to the EL connectionwiring electrodes 15 via through holes formed in the protectiveinsulating film 22 having a film thickness of 200 nm and composed ofSi₃N₄.

[0172] Organic LEDs having the above layered structure are formed abovethe anode electrodes 13.

[0173] Third Embodiment

[0174]FIG. 10 is a circuit diagram showing equivalent networks forpixels in a display device according to a third embodiment of theinvention, and FIG. 11 is a plan view showing a pixel arrangement in thedisplay device according to the third embodiment of the invention.

[0175] With the self-luminescence display device according to theembodiment, an EL element OLED(m, n) in row m and column n is driven byfive parallel EL drive TFTs formed in total five regions of pixels inrow m and column (n−2), row m and column (n−1), row m and column (n+1),and row m and column (n+2) as well as in row m and column n.

[0176] Since the number in parallel is five, such averaging greatlycontributes to improvement in uniformity, which makes it possible toobtain an enhanced uniform display characteristics.

[0177] Fourth Embodiment

[0178]FIG. 12 is a circuit diagram showing equivalent networks forpixels in a display device according to a fourth embodiment of theinvention, and FIG. 13 is a plan view showing a pixel arrangement in thedisplay device according to the fourth embodiment of the invention.

[0179] With the self-luminescence display device according to theembodiment, an EL element OLED(m, n) in row m and column n is driven bysix parallel EL drive TFTs formed in total six regions of pixels in rowm and column (n+1), row m and column (n+2), row m and column (n+3), rowm and column (n+4), and row m and column (n+5) as well as in row m andcolumn n.

[0180] Since the number in parallel is six, such averaging greatlycontributes to improvement in uniformity, which makes it possible toobtain an enhanced uniform display characteristics.

[0181] Also, the embodiment adopts a configuration, in which lightemitted from the EL elements is taken not from a side of the substratebut a side of a front surface.

[0182] When the number of TFTs in pixels is increased as in theembodiment, it becomes difficult to ensure an area of those EL elements,which contribute to emission of light.

[0183] In such case, that configuration, in which light is taken fromthe side of a front surface, is advantageous.

[0184]FIG. 14 is a cross sectional view showing a cross-sectionalstructure cut along the line X-X′ shown in FIG. 13. As shown in FIG. 14,a buffer Si₃N₄ film 200 having a thickness of 50 nm and a buffer SiO₂film 2 having a thickness of 100 nm are formed on a non-alkali glasssubstrate 1 having a thickness of 0.5 mm and a strain temperature ofabout 670° C.

[0185] Formed on the buffer SiO₂ film 2 is a polycrystal Si film 30having a thickness of 50 nm and corresponding to the charge-storagecapacitance Cst(m, n), and formed on the poly-Si film 30 through a gateinsulating film 20 formed from SiO₂ are gate wiring electrodes 14 of theEL drive TFTs composed of Mo.

[0186] The gate wiring electrode 14 of the EL drive TFT (Qd3(m, n))shown in FIG. 14 is shown as its portion being extended below anassociated pixel as shown in FIG. 13, and the poly-Si film 30 shown inFIG. 14 is electrically connected to the anode current feeding wiringelectrode An through the contact hole as shown in FIG. 13.

[0187] The anode current feeding wiring electrode An is formed above thegate wiring electrode 14 of the EL drive TFT with an interlayerinsulating film 21 formed from SiO₂ therebetween. The anode currentfeeding wiring electrode An is of a three-layered electrode structurecomposed of Mo (110 a), Al (110 b), and Mo (110 c).

[0188] Also, a picture signal wiring electrode Dn and a reflective film17 are also formed on the same layer as the anode current feeding wiringelectrode An.

[0189] The picture signal wiring electrode Dn is of a three-layeredelectrode structure composed of Mo (11 a), Al (11 b), and Mo (11 c), andthe reflective film 17 is also of a three-layered electrode structurecomposed of Mo/Al/Mo.

[0190] The reflective film 17 is connected to an anode electrode 13 viaopenings (CH1, Cf2 in FIG. 13) formed in a protective insulating film 22having a film thickness of 200 nm and composed of Si₃N₄.

[0191] The reflective film 17 is formed in a region in, for example, apixel in row m and column n, except for that region, in which a switchTFT and an EL drive TFT (Qd1(m, n)) are formed.

[0192] The reflective film 17 serves to reflect light emitted from an ELelement to a front surface and constitutes a part of the charge-storagecapacitance Cst(m, n) between it and the poly-Si film 30 when the ELdrive TFT (Qd3(m, n)) is ON.

[0193] Accordingly, in the embodiment, the charge-storage capacitanceCst(m, n) is defined by a capacitative element formed by the gateinsulating film 20 between the gate wiring electrode 14 and the poly-Sifilm 30, and a capacitative element formed by an interlayer insulatingfilm 21 between the reflective film 17 and the poly-Si film 30.

[0194] All these constituents are covered by a protective insulatingfilm 22 having a film thickness of 200 nm and formed from Si₃N₄, onwhich film is formed an anode electrode 13 composed of an indium-tinoxide (ITO).

[0195] Further, an organic insulating film 23 having a film thickness of2 μm and containing polyimide as its main component is formed on theanode electrode 13, and the organic insulating film 23 is providedsubstantially centrally of the anode electrode 13 with an opening.

[0196] Formed on the anode electrode 13 and the organic insulating film23 is an electron hole transport layer 300 having a film thickness of150 nm and composed of triphenyldiamine (TPD), and formed on the layerare a red EL luminescent layer 301R and composed of a tris(8-hydroxyquinoline) aluminum (Alq3) having a film thickness of 30 nmand doped with DCJTB and rubrene, and an electron hole transport layer(not shown) having a film thickness of 30 nm and composed of Alq3.

[0197] Formed above the electron hole transport layer through LiF havinga film thickness of 0.8 nm are 2-9-dimethyl-4, 7diphenyl-1,10-phenanthroline (BCP) having a film thickness of 7 nm and ITO having afilm thickness of 77 nm to constitute a transparent cathode electrode302.

[0198] Electron holes injected from the anode electrode 13 and electronsinjected from the cathode electrode 302 make radiational reunion in thered EL luminescent layer 301R to cause emission.

[0199] Light generated is emitted toward the transparent cathodeelectrode.

[0200] Arranged in adjacent pixels are blue dots and green dots, onwhich a blue EL luminescent layer 301B and a green EL luminescent layer301G are formed in place of a red EL luminescent layer.

[0201] The blue EL luminescent layer is DPVBi doped with BCzVBi having afilm thickness of 15 nm, and the green EL luminescent layer is Alq3doped with coumarin 540 having a film thickness of 30 nm.

[0202]FIG. 15 is a graph indicating the relationship between the numberN of parallel EL drive TFTs and dispersion (MAX−MIN)/(MAX+MIN) inluminance among pixels.

[0203] As seen from the graph in FIG. 15, dispersion in luminance in thecase of N=3 can be reduced to about a half of that in the case of N=1.

[0204] Theoretically, it is presumed that with respect to the parallelnumber N, the degree of dispersion is decreased inversely proportionalto {square root}N.

[0205] According to the graph in FIG. 15, a dispersion decreasing effectas appropriately presumed theoretically is obtained.

[0206] Fifth Embodiment

[0207] An entire configuration of the display device according to theinvention in a fifth embodiment of the invention will be described belowwith reference to FIGS. 16 to 18.

[0208] Formed on the glass substrate 1 are an active matrix AMXconstituted by TFTS, a vertical scanning circuit VDRV and a picturesignal circuit HDRV.

[0209] The cathode electrode 302 of the EL element OLED is connected toa wiring 401 taken out and formed on the glass substrate 1 through acontact hole in a contact area 400 and then to an external connectionterminal PAD.

[0210] Also, all anode current feeding wiring electrodes A provided inrespective columns in pixels are connected outside pixel regions to theexternal connection terminal PAD through a taken-out electrode 402.

[0211] The embodiment has a feature in that the contact area 400 isarranged between the active matrix AMX and the external connectionterminal PAD and the picture signal circuit HDRV is disposed on anopposite side of the active matrix AMX to the external connectionterminal PAD.

[0212] With such arrangement, the taken-out wiring 401 extending fromthe external connection terminal PAD to the contact area 400 can be madeshort, so that voltage drop and power consumption caused by resistanceof the taken-out wiring can be minimized.

[0213] Since current from the EL elements OLED in all pixels flowsthrough the taken-out wiring of the cathode electrode 302, reduction inresistance of the taken-out wiring is important.

[0214] Meanwhile, since current flowing through a power source wiringand ground wiring to the picture signal circuit HDRV is small ascompared with current flowing through the EL elements OLED, nosignificant problem is caused even when such wirings are lengthened moreor less.

[0215]FIG. 17 is an exploded, perspective view showing the entiredisplay device shown in FIG. 16.

[0216] A seal glass 600 is mounted through a seal SHL on the glasssubstrate 1, on which the cathode electrode 302 of the EL elements OLEDis formed, whereby the EL elements OLED are not exposed to outside air.

[0217] Used for the seal SHL is an ultraviolet hardening-type resin, inwhich fiber glass having a diameter of 10 μm is dispersed.

[0218] The seal glass and the glass substrate 1 substantially correspondto each other in external shape at three sides except aside, from whichthe external connection terminal PAD is taken out, so that the entirepanel is made minimum in external dimension.

[0219]FIG. 18 is a cross sectional view showing a cross-sectionalstructure of the display device shown in FIG. 16.

[0220] A chemical adsorbent 602 for absorbing moisture entering fromoutside and a gas emitted from a material, which forms the EL elementsOLED, is held on projections provided in the seal glass 600 by means ofa tape 601.

[0221] Calcium oxide (CaO) was used as the chemical adsorbent.

[0222] Also, a dry N2 gas, from which moisture is removed up to thedew-point of −78° C., is sealed in a cavity in the seal glass 600.

[0223] Sixth Embodiment

[0224] A manufacturing process, according to a sixth embodiment of theinvention, for an active matrix substrate in the display deviceaccording to the second embodiment will be described below withreference to FIGS. 19 to 27.

[0225] First, the plasma CVD method making use of a mixture gas of SiH₄,NH₃ and N₂ is used to form a Si₃N₄ film 200 having a thickness of 50 nmafter a non-alkali glass substrate 1 having a thickness of 0.5 mm, alength of 750 mm and a width of 950 mm and a strain temperature of about670° C. is cleaned.

[0226] Subsequently, the plasma CVD method making use of a mixture gasof tetraethoxysilane and O₂ is used to form a SiO₂ film 2 having athickness of 120 nm.

[0227] In addition, both Si₃N₄ and SiO₂ are formed at temperature of400° C.

[0228] Then a substantially intrinsic hydro-amorphous silicon film 35having a thickness of 50 nm is formed on the SiO₂ film 2 by the plasmaCVD method making use of a mixture gas of SiH₄ and Ar.

[0229] A deposition temperature was 400° C. and an amount of hydrogenwas about 5 atomic % immediately after deposition.

[0230] Subsequently, the substrate is annealed at 450° C. for about 30minutes whereby hydrogen in the hydro-amorphous silicon film 35 iscaused to be released.

[0231] Subsequently, the plasma CVD method making use of a mixture gasof tetraethoxysilane and O₂ is used to form a SiO₂ film 201 having athickness of 100 nm, and then boron (B+) is implanted in a dose 5×10¹²(atoms/cm²) at acceleration voltage of 40 KeV by ion-implantation.

[0232] Boron serves to adjust a threshold voltage of TFT (see FIG. 19).

[0233] Subsequently, the SiO₂ film 201 is removed by a bufferhydrofluoric acid, and pulse excimer laser of a wavelength of 308 nmprocessed in the form of stripe having a short side of 0.3 mm and a longside of 300 mm is irradiated on the amorphous silicon film 35 at afluence of 450 mJ/cm² while moving at 10 μm in a direction along theshort side, whereby the amorphous silicon film 35 is melted andrecrystallized to provide a P type polycrystal silicon film 30 (see FIG.20).

[0234] At this time, dispersion in the TFT characteristics caused bydispersion in crystal quality of the polycrystal silicon in a scanningdirection of laser beam generally tends to become greater thandispersion in a direction perpendicular to the scanning direction oflaser beam.

[0235] Therefore, a great effect is obtained by arranging a plurality ofEL drive TFTs in parallel in the scanning direction of laser beam.

[0236] The scanning direction of laser beam shown by arrows in FIGS. 3or 6 indicates this, and the plurality of EL drive TFTs are arrangedsubstantially in parallel in the scanning direction of laser beam.

[0237] The same is with the embodiment shown in FIGS. 10 and 12.

[0238] Subsequently, the reactive ion etching method making use of CF₄is used to process the P type polycrystal silicon film 30 in apredetermined form to obtain TFTs and a wiring pattern (P typepolycrystal silicon film 30) except the TFTs.

[0239] Subsequently, the plasma CVD method making use of a mixture gasof tetraethoxysilane and O₂ is used to form SiO₂ having a thickness of100 nm to form a gate insulating film 20.

[0240] Subsequently, after the sputtering method is used to form a Mofilm having a thickness of 200 nm, an ordinary photolithography methodis used to form a predetermined resist pattern PR on the Mo film, andthe reactive ion etching method making use of CF₄ is used to process theMo film in a predetermined form to obtain gate electrodes 10N for N typeTFTs.

[0241] Subsequently, while the resist pattern PR used in etching isleft, phosphorus (P) ions are implanted in a dose 10¹⁵ (atoms/cm²) atacceleration voltage of 60 KeV by ion-implantation to form regions ofsource electrodes and drain electrodes for N type TFTs (see rightwardand central portions in FIG. 21).

[0242] At this time, all the elements are protected by patterns of theMo film and the photoresist film PR to prevent phosphorus ions frombeing implanted into the P type TFTs (see a leftward portion in FIG.21).

[0243] Subsequently, while the resist pattern is left, the substrate isprocessed by a mixed acid and the Mo electrodes thus processed aresubjected to side etching whereby the pattern is slimmed and the resistis removed, after which P ions are implanted in a dose 2×10¹³(atoms/cm²) at acceleration voltage of 65 KeV by ion-implantation toform LDD regions for N type TFTS.

[0244] The LDD regions are controlled in length by a side etching timewith the mixed acid (see FIG. 22).

[0245] Subsequently, a predetermined resist pattern is formed on the Mofilm, and the reactive ion etching method making use of CF₄ is used toobtain gate electrodes 10P for P type TFTs and a wiring pattern (gatewiring electrode 14) except the TFTs.

[0246] Using the gate electrodes 10P for P type TFTs as a mask, boronions are implanted in a dose 10¹⁵ (atoms/cm²) at acceleration voltage of40 KeV by ion-implantation to form regions of source electrodes anddrain electrodes for P type TFTs.

[0247] At this time, all N type TFTs are protected by the photoresistpattern PR to be protected from the etching gas and prevent boron ionsfrom being implanted thereinto (see FIG. 23).

[0248] After the photoresist is removed, ultraviolet light from anexcimer lamp or metal halide lamp is irradiated to activate impuritiesimplanted by the rapid thermal anneal (RTA) method (see FIG. 24).

[0249] Subsequently, the plasma CVD method making use of a mixture gasof tetraethoxysilane and oxygen is used to form SiO₂ having a filmthickness of 500 nm to form an interlayer insulating film 21.

[0250] After a predetermined resist pattern is formed, the wet etchingmethod making use of a mixed acid is used to form contact through holesin the interlayer insulating film 21.

[0251] Subsequently, after the sputtering method is used to sequentiallylaminate Mo film of 50 nm, an Al—Nd alloy of 500 nm and Mo of 50 nm, apredetermined resist pattern is formed, and then the reactive ionetching method making use of a mixed gas of BCl₃ and Cl₂ performsetching collectively to fabricate picture signal wiring electrodes D,anode current feeding wiring electrodes A, connection wiring electrodes12 and EL connection wiring electrodes 15 (see FIG. 25).

[0252] Subsequently, the plasma CVD method making use of a mixture gasof SiH₄, NH₃ and N₂ is used to form a Si₃N₄ film having a thickness of400 nm to make the same a protective insulating film 22.

[0253] After a predetermined photoresist pattern is formed, the dryetching method making use of SF₆ is used to form contact through holesin the protective insulating film 22.

[0254] Succeedingly, the sputtering method is used to form an ITO filmof 70 nm and the wet etching method making use of a mixed acid is usedto process the film in a predetermined shape to form anode electrode 13for EL elements OLED (see FIG. 26).

[0255] Finally, the spin coating method is used to coat a photosensitivepolyimide resin in a film thickness of about 3.5 μm, and a predeterminedmask is used to perform exposure and development to remove the polyimideresin in those portions of the anode electrode, on which EL elementsOLED are formed, thereafter performing baking the polyimide resin for 30minutes at 350° C. to form an organic insulating film 23 having a filmthickness of 2.3 μm (see FIG. 27).

[0256] The organic insulating film 23 is formed to cover ends of theanode electrode 13 to prevent the EL elements OLED from being broken byfield concentration at ends of the ITO electrodes when a very thinorganic film forming the EL elements OLED is formed on the anodeelectrode.

[0257] A process of forming EL elements on an active matrix substratefabricated by the above processes will be described below.

[0258] The active matrix substrate is set in a vacuum deposition device,and first introduced into a preheating chamber to be baked under vacuumfor one hour at 200° C., whereby moisture adsorbing to surfaces of thesubstrate and moisture contained in the organic insulating film 23 areremoved.

[0259] Subsequently, ultraviolet light is irradiated at the intensity of60 mW/cm² for 60 seconds in an atmosphere containing oxygen to removeorganic substances on the surfaces of the anode electrode.

[0260] Subsequently, the active matrix substrate is moved into apretreatment chamber to be subjected to O₂ plasma processing whereby thesurfaces of the anode electrode are adjusted in work function.

[0261] The processing condition involves 60 seconds at the RF power of200 W.

[0262] This processing adjusts the work function of ITOs being the anodeelectrode 13 at 5.1 to 5.2 eV, and decreases a barrier level whenelectrons are injected into an electron hole transport material, wherebyan efficiency of injection can be enhanced.

[0263] Subsequently, the active matrix substrate is moved into a firstdeposition chamber to be subjected to mask deposition with a mask, inwhich an electron hole transport layer is formed on an entire displaysurface.

[0264] Triphenyldiamine (TPD) is used for a material of the electronhole transport layer.

[0265] Besides this, for example, α-NPD can be used.

[0266] The electron hole transport layer has a film thickness of 150 nm.

[0267] Subsequently, the active matrix substrate is moved into a seconddeposition chamber to be subjected to mask deposition of luminescentmaterials for respective RGBs.

[0268] In deposition of different luminescent materials, predeterminedmaterials are formed in dot positions of respective RGBs by first makingregister between dots representative of blue color and openings in adeposition mask, forming a blue material, shifting the deposition mask apitch of one dot within the deposition chamber, making deposition of agreen material, and further moving the deposition mask similarly to makedeposition of a red material.

[0269] Subsequently, the active matrix substrate is moved into a thirddeposition chamber to form a cathode electrode 302.

[0270] In order to enhance an efficiency of electron injection for theorganic layer, the cathode electrode 302 is formed such that after LiFis formed to have a film thickness of around 0.8 nm, Al is formed tohave a thickness of 150 nm.

[0271] Subsequently, the active matrix substrate is moved into a sealchamber, a seal glass having been beforehand baked like the activematrix substrate for dehydration is bonded to the active matrixsubstrate with an ultraviolet hardening-type resin therebetween, andultraviolet light is irradiated on a back surface of the active matrixsubstrate to cure the resin. At this time, a chemical adsorbent isinserted into an air gap in the seal glass.

[0272] All the preceding steps after setting of the active matrixsubstrate must be effected in a state, in which the active matrixsubstrate is not exposed to the atmospheric air.

[0273] Finally, the active matrix substrate, to which the seal glass isbonded, is taken out to be cut into a predetermined size, and driverLSIs are loaded on the substrate to finish a panel.

[0274] While the invention having been thought of by the inventors ofthis application has been concretely described on the basis of theembodiments, it is not limited to the embodiments but can be of coursemodified within a scope not departing from the gist thereof.

[0275] Effects obtained by typical configurations of the inventiondisclosed in this application are simply described below.

[0276] (1) It is possible in a self-luminescence display deviceaccording to the invention to obtain a uniform display screen free ofunevenness.

[0277] (2) It is possible in a self-luminescence display deviceaccording to the invention to reduce voltage drop and power consumptioncaused by resistance of the taken-out wiring of the cathode electrodes.

What is claimed is:
 1. A display device comprising a plurality of pixelshaving current drive type luminescent elements, and parallel-connected n(n≧2) thin-film transistors to feed a drive current to the respectivecurrent drive type luminescent elements, and wherein theparallel-connected n thin-film transistors are arranged in differentpixels.
 2. The display device according to claim 1, wherein theparallel-connected n thin-film transistors are arranged in pixelsadjacent to one another.
 3. The display device according to claim 2,comprising a first region including said parallel-connected n thin-filmtransistors arranged in said pixels adjacent to one another in a firstdirection and a second region including dummy pixels, wherein saidsecond region is located on at least one side of said first region alongsaid first direction.
 4. The display device according to claim 2,wherein n is a number in a range between 3 and 12, inclusive.
 5. Adisplay device comprising a plurality of pixels having current drivetype luminescent elements, and n (n≧2) thin-film transistors connectedin parallel to feed a drive current to the respective current drive typeluminescent elements, and wherein the parallel-connected n thin-filmtransistors are arranged in different pixels in a scanning direction ofa laser beam, which laser beam is used when the thin-film transistorsare fabricated.
 6. The display device according to claim 5, whereinchannel layers of the parallel-connected n thin-film transistors arecomprised of a polycrystal silicon film, which is fabricated byirradiating a laser beam on an amorphous silicon film.
 7. The displaydevice according to claim 5, wherein the parallel-connected n thin-filmtransistors are arranged in pixels adjacent to one another.
 8. Thedisplay device according to claim 7, comprising a first region includingsaid parallel-connected n thin-film transistors arranged in said pixelsadjacent to one another in a first direction and a second regionincluding dummy pixels, wherein said second region is located on atleast one side of said first region along said first direction.
 9. Thedisplay device according to claim 7, wherein n is a number in a rangebetween 3 and 12, inclusive.
 10. A display device comprising a pluralityof pixels having current drive type luminescent elements, m (m≧2)current feeding wiring electrodes, and n (n≧2) thin-film transistorsconnected in parallel to feed drive current to the respective currentdrive type luminescent elements, and wherein the parallel-connected nthin-film transistors are connected to different current feeding wiringelectrodes, respectively.
 11. The display device according to claim 10,wherein the plurality of pixels are arranged in a matrix configurationand one of the m current feeding wiring electrodes is provided for eachrow of pixels, respectively.
 12. A display device comprising a pluralityof pixels having current drive type luminescent elements, m (m≧2)current feeding wiring electrodes, and n (n≧2) thin-film transistorsconnected in parallel to feed drive current to the respective currentdrive type luminescent elements, and wherein the parallel-connected nthin-film transistors are connected to different current feeding wiringelectrodes, respectively, and wiring layers to feed the drive current tothe respective current drive type luminescent elements are comprised ofsemiconductor layers formed integrally with channel layers of therespective thin-film transistors and connected electrically to thechannel layers of the respective thin-film transistors.
 13. The displaydevice according to claim 12, wherein the plurality of pixels arearranged in a matrix configuration and one of the m current feedingwiring electrodes is provided for each row of pixels, respectively. 14.A display device comprising a plurality of pixels having current drivetype luminescent elements, parallel-connected n (n≧2) thin-filmtransistors to feed drive current to the respective current drive typeluminescent elements, and holding capacitances connected to respectivegate electrodes of the parallel-connected n thin-film transistors tohold a picture signal voltage, and wherein each of the holdingcapacitances is arranged in a pixel which is different from a pixel inwhich the current drive type luminescent element supplied with a drivecurrent from the corresponding parallel-connected n thin-film transistorconnected to the holding capacitance is arranged.
 15. The display deviceaccording to claim 14, wherein each of the holding capacitances isarranged in a region outside a luminescent region within a pixel whichis different from a pixel in which the current drive type luminescentelement supplied with a drive current from the correspondingparallel-connected n thin-film transistor connected to the holdingcapacitance is arranged.
 16. The display device according to claim 14,further comprising (m≧2) current feeding wiring electrodes and whereinthe holding capacitances are arranged below them current feeding wiringelectrodes.
 17. The display device according to claim 16, wherein one ofelectrodes constituting the holding capacitances is comprised ofsemiconductor layers formed integrally with channel layers of theparallel-connected n thin film transistors and connected electrically toone of the m current feeding wiring electrodes.
 18. The display deviceaccording to claim 17, wherein another of electrodes constituting theholding capacitances is comprised of wiring layers formed integrallywith gate electrodes of the parallel-connected n thin-film transistorsconnected electrically to the gate electrodes of the parallel-connectedn thin-film transistors, the wiring layers being opposed to thesemiconductor layers with an insulating film therebetween.
 19. Thedisplay device according to claim 16, wherein the plurality of pixelsare arranged in a matrix configuration and one of the m current feedingwiring electrodes is provided for each row of pixels, respectively. 20.A display device comprising a plurality of pixels each having currentdrive type luminescent elements, and a plurality of thin-filmtransistors to feed a drive current to the respective current drive typeluminescent elements; and a reflective layer disposed between asubstrate and the current drive type luminescent elements to cover atleast a part of the n thin-film transistors.
 21. The display deviceaccording to claim 20, wherein each pixel comprises parallel-connected nthin-film transistors to feed a drive current to the respective currentdrive type luminescent elements and wherein the parallel-connected nthin-film transistors are arranged in different pixels.
 22. The displaydevice according to claim 20, wherein the parallel-connected n thin-filmtransistors are arranged in different pixels in a scanning direction ofa laser beam, which laser beam is used when the thin-film transistorsare fabricated.
 23. The display device according to claim 22, whereinchannel layers of the parallel-connected n thin-film transistors arecomprised of a polycrystal silicon film, which is fabricated byirradiating a laser beam on an amorphous silicon film.
 24. The displaydevice according to claim 21, wherein the parallel-connected n thin-filmtransistors are arranged in pixels adjacent to one another.
 25. Thedisplay device according to claim 24, comprising a first regionincluding said parallel-connected n thin-film transistors arranged insaid pixels adjacent to one another in a first direction and a secondregion including dummy pixels, wherein said second region is located onat least one side of said first region along said first direction. 26.The display device according to claim 24, wherein n is a number in arange between 3 and 12, inclusive.
 27. A display device comprising aplurality of pixels having current drive type luminescent elements, and(parallel-connected) n (n≧2) thin-film transistors to feed a drivecurrent to the respective current drive type luminescent elements; areflective layer disposed below the current drive type luminescentelements to cover at least a part of the n thin-film transistors; m(m≧2) current feeding wiring electrodes, wherein the parallel-connectedn thin-film transistors, respectively, are connected to differentcurrent feeding wiring electrode.
 28. The display device according toclaim 27, wherein the plurality of pixels are arranged in a matrixconfiguration and the m current feeding wiring electrodes are providedfor each row of pixels.
 29. A display device comprising a plurality ofpixels having current drive type luminescent elements, andparallel-connected n (n≧2) thin-film transistors to feed a drive currentto the respective current drive type luminescent elements; a reflectivelayer disposed below the current drive type luminescent elements tocover at least a part of the n thin-film transistors; and m (m≧2)current feeding wiring electrodes, wherein the parallel-connected nthin-film transistors, respectively, are connected to different currentfeeding wiring electrodes and wiring layers to feed the drive current tothe respective current drive type luminescent elements and wherein thewiring layer are comprised of semiconductor layers formed integrallywith channel layers of the respective thin-film transistors andconnected electrically to the channel layers of the respective thin-filmtransistors.
 30. The display device according to claim 29, wherein theplurality of pixels are arranged in a matrix configuration and the mcurrent feeding wiring electrodes are provided for each row of pixels.31. A display device comprising current drive type luminescent elements,thin-film transistors to feed a drive current to the current drive typeluminescent elements, holding capacitances connected to gate electrodesof the thin-film transistors to hold a picture signal voltage, whichcontrols a drive current fed to the current drive type luminescentelements, for one frame, and a reflective layer disposed below thecurrent drive type luminescent elements to cover the thin-filmtransistors and the holding capacitances.
 32. A display devicecomprising a plurality of pixels each having current drive typeluminescent elements, and parallel-connected n (n≧2) thin-filmtransistors to feed a drive current to the respective current drive typeluminescent elements; a reflective layer disposed below the currentdrive type luminescent elements to cover at least a part of the nthin-film transistors, and holding capacitances connected to respectivegate electrodes of the parallel-connected n thin-film transistors tohold a picture signal voltage, and wherein each of the holdingcapacitances is arranged in a pixel which is different from a pixel inwhich the current drive type luminescent elements supplied with a drivecurrent from the corresponding parallel-connected n thin-filmtransistors connected to the holding capacitance is arranged.
 33. Thedisplay device according to claim 32, further comprising m (m≧2) currentfeeding wiring electrodes, and wherein one of electrodes constitutingthe holding capacitances is comprised of semiconductor layers formedintegrally with channel layers of the parallel-connected n thin-filmtransistors and connected electrically to one of the m current feedingwiring electrodes.
 34. The display device according to claim 33, whereinthe other of electrodes constituting the holding capacitances iscomprised of wiring layers formed integrally with gate electrodes of theparallel-connected n thin-film transistors connected electrically to thegate electrodes of the parallel-connected n thin-film transistors, thewiring layers being opposed to the semiconductor layers with aninsulating film therebetween.
 35. A display device comprising asubstrate, a plurality of current drive type luminescent elementsprovided on the substrate, an externally connected terminal unitprovided on an edge of a side of the substrate, and take-out wiringsconnected electrically to cathode electrodes of the plurality of currentdrive type luminescent elements in a contact area provided between theexternally connected terminal unit and an area in which the plurality ofcurrent drive type luminescent elements are provided, and connectedelectrically to a terminal of the externally connected terminal unit.36. A display device comprising a plurality of pixels, each of theplurality of pixels comprises a luminescent element having a first widthin a first direction, wherein each of the luminescent element isconnected to a dispersion decreasing circuit, which extends across anarea having a width larger than the first width.
 37. A display deviceaccording to claim 36, wherein the dispersion decrease circuit comprisesa plurality of parallel connected thin-film transistors each connectedto the same luminescent element.
 38. A display device comprising aplurality of pixels, each of the plurality of pixels comprises aluminescent element and a first width in a first direction, wherein eachof the luminescent element is connected to a means for decreasingdispersion of the display device, wherein said dispersion decreasingmeans extends across an area having a width larger than the first width.39. A display device according to claim 38, wherein said dispersiondecreasing means comprises a plurality of parallel connected thin-filmtransistors each connected to the same luminescent element.